Mode I fracture toughness is a key material property that is used in modeling the damage tolerance of a composite part. Current standard measurement practice involves using a double cantilever beam (DCB) test where a precrack is introduced into a laminate and the crack is opened in tension. Load, crack opening displacement, and crack length are measured as the crack extends down the length of the coupon. Despite careful effort, the crack length can be difficult to determine accurately and the resulting calculated fracture toughness values (G1c) can have significant scatter. In this study, standard fixed width DCB tests are compared to width- tapered DCB tests and in both cases the fracture toughness is calculated with the compliance method. The advantage of using a width-tapered DCB coupon is that stable crack growth occurs at a constant load so measurement of the crack length or crack tip opening displacement is unnecessary. In this study the equivalence of both the fixed width and width-tapered DCB tests is shown. Therefore, in situations where crack length or crack tip opening measurements can be difficult to obtain accurately (high rate, elevated temperature) the width-tapered DCB can be quite useful.
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